55 dB CNR over 50 km of fibre in an 80-channel externally-modulatedAM-CATV system without optical amplification

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Abstract
The authors demonstrate supertrunking quality performance in an externally modulated 1550 nm AM-CATV system over a 50 km fibre link for the first time without the use of optical amplification. This performance has been enabled by a high-power 1550 nm DFB laser module (17 dBm fibre-coupled output) and differential detection. High power (9.5 dBm), low noise signals from the complementary outputs of an LiNbO3 intensity modulator were launched into two parallel fibres. After 50 km, RF subcarriers from two receivers recombined in phase increasing the carrier to noise ratio by 3 dB. The above configuration has allowed 80 NTSC channels to be transmitted with CNR > 55 dB, CSO, CTB < –65 dBc.